Deformable scaffolding multicellular stent

ABSTRACT

A plastically deformable stent for implantation within a body passage includes a plurality of cylindrical segments, and a plurality of connectors extending between adjacent segments. Each segment has an alternating pattern of curvilinear elements extending about its circumference, including first and second sets of curvilinear elements having different resistances to expansion, and preferably defining “U” shapes with alternating lengths that are connected to one another to define a substantially sinusoidal pattern. The connectors define a sinusoidal shape adapted to extend and compress axially substantially evenly when the adjacent segments are subjected to bending. The stent may be delivered on a device including an elongate member with a nose cone, an expandable member, and a proximal shoulder thereon, and an outer sheath for slidably receiving the elongate member therein. The outer sheath and/or nose cone may have perfusion holes for allowing continued perfusion of fluid during stent delivery. The device may be used in a method for implanting a stent within a curved region of a body passage, particularly for creating and/or maintaining a channel connecting a vein to an adjacent artery, preferably in the coronary system.

This application is a continuation-in-part of application Ser. No.08/970,694 filed Nov. 14, 1997, the disclosure of which is expresslyincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to implantable devices for usewithin the cardiovascular system, and more particularly to deformableprostheses for implantation within and/or between blood vessels, and tomethods of using them.

BACKGROUND

A variety of stents are known for use within arteries of a patient fortreating stenoses, strictures, aneurysms, and the like. For example, astent may be implanted within a partially occluded region of an arteryto retain stenotic material beneath the stent and/or to open the lumenof the artery to improve blood flow therethrough.

Stents generally have a substantially cylindrical shape and areexpandable between a contracted condition for facilitating delivery andan enlarged condition for engaging the vessel wall after deploymentwithin the artery. Stents may be self-expanding, i.e., they may bebiased to the enlarged condition but restrained in the contractedcondition during delivery, for example within a sheath. Alternatively,stents may be substantially malleable or plastically deformable, i.e.,the stent may be delivered in a contracted condition on a deliverycatheter, and expanded by a balloon on the delivery catheter, until itplastically deforms into the enlarged condition.

Many stents include a plurality of segments or cells that are separatedby one or more connectors extending between adjacent segments. Forexample, U.S. Pat. No. 5,104,404 discloses an expandable stent thatincludes a number of cylindrical segments, with single hinges connectingadjacent segments. Because of the rigidity of the individual segments ofthe stent, the hinges are intended to provide articulation between theadjacent segments.

When the stent is deployed within a curved portion of a vessel, theindividual segments substantially resist bending to conform to thecurvature of the vessel. The articulation provided by the hinges allowssome conformity with the curvature of the vessel; however, the hingesmay create gaps between the segments and/or may cause the segments tooverlap one another. Material, such as stenotic material on the vesselwall, may extend through the gaps into the vessel lumen, possiblyobstructing blood flow and/or breaking loose and traveling downstreamwhere they may cause substantial damage to the patient being treated.

To reduce the likelihood of gaps occurring, some stents provide a numberof connectors extending between adjacent segments. Increasing the numberof connectors substantially, however, may increase the rigidity of thestent, which may cause problems during stent delivery. For example, whenthe stent is being delivered along a circuitous arterial path, therigidity of the stent, particularly in its contracted condition, mayimpair advancement of the stent around tight bends in the artery.

Alternatively, some stents may include flexible connectors that aredeformed when the segments are expanded to the enlarged condition. Theresulting connectors may deform substantially to become part of thestent structure, i.e., they may deform substantially such that they losetheir flexibility and are then unable to accommodate transverse bendingforces.

In addition, some known stents have substantial gaps within theindividual segments themselves or between the connectors, and so may noteffectively “scaffold” the underlying vessel wall, i.e., may not supportthe vessel wall to maintain a desired open lumen cross-section and/ormay expose material extending from the vessel wall into the bloodstream.Initially, stents in their contracted condition may have substantiallyfew gaps within the individual segments, i.e., peripherally about thecircumference of the segments. When the stents are expanded to theirenlarged condition, however, substantial gaps may be created at one orpoints along the circumference either within the segments, due to thedesign of the segments or to uneven expansion of the individualsegments, or between the connectors.

The risk of uneven radial expansion may be particularly problematic withrespect to balloon-expandable stents due to the nature of the balloonsgenerally used. Balloon-expandable stents are typically manuallycompressed onto an inelastic balloon provided on the delivery catheter.Because of its inelasticity, the balloon is typically rolledcircumferentially or otherwise wrapped around the catheter before thestent is placed over it, thereby attempting to ensure that the balloonis not snagged or damaged during delivery or deployment of the stent.

Once the stent is delivered intraluminally to a desired region within avessel, the balloon is inflated to expand the stent to its enlargedcondition. As the balloon unwraps during inflation, it may subject thestent to radial forces that are not substantially even along the lengthand/or the circumference of the stent. More particularly, some regionsof the balloon may expand more quickly than other regions that have notyet fully unwrapped, causing localized heightened radial forces whichmay cause uneven radial expansion of the stent. Because of the unevenlydistributed forces, a portion of the circumference of the stentoverlying an initially unwrapped region of the balloon may be expandedgreater than an adjacent portion where the balloon has not yet fullyunwrapped. This may substantially increase the risk of over-expandingportions of the stent, and thereby creating gaps in the over-expandedportions.

In an effort to provide a uniform enlarged condition, stents generallyhave a substantially uniform pattern extending about the circumferenceof the individual segments, and generally have segments of equallengths. Because of the uneven radial forces which may be encounteredduring expansion, however, these stents may not expand substantiallyuniformly despite the intended result of their uniform designs. Thisproblem may be further exacerbated because individual stents aregenerally intended to be expanded to a range of potential enlargedsizes, for example, between 3.0 mm and 5.5 mm. While at the upper end ofthe range, the radial forces may become more even and expand the stentmore uniformly, the stent may be prone to uneven expansion at the lowerend of the range, where localized heightened radial forces are morelikely to occur.

Accordingly, it is believed that there is a need for stents which moreeffectively scaffold the vessel wall and/or which substantially evenlyengage vessel walls, particularly within curved vessel regions, and formethods and systems using such stents.

SUMMARY OF THE INVENTION

The present invention is directed to implantable devices for use withinbody passages, particularly within the cardiovascular system, and moreparticularly to deformable prostheses for implantation within and/orbetween blood vessels, and to methods of using them to create and/ormaintain connections between adjacent blood vessels.

In one aspect of the present invention, a stent is provided forimplantation within a body passage that includes a plurality ofexpandable segments defining a circumference and a longitudinal axis,and a connector extending between adjacent segments. Each segmentincludes an alternating pattern of curvilinear elements extending aboutthe circumference.

In a preferred embodiment, the alternating pattern includes a first setof curvilinear elements having a first resistance to expansion and asecond set of curvilinear elements having a second resistance toexpansion substantially higher than the first resistance to expansion.Consequently, each segment is expandable between a contracted condition,a first or intermediate expanded condition, and a second or finalexpanded condition. Preferably, the first expanded condition is achievedwhen a radial force exceeding the first resistance to expansion isapplied to the segment, and the second expanded condition is achievedwhen a radial force exceeding the second resistance to expansion isapplied to the segment.

More preferably, the first and second sets of curvilinear elements aresubstantially “U” shaped elements having first and second longitudinallengths, respectively, the second longitudinal length beingsubstantially less than the first longitudinal length. The substantially“U” shaped elements of the first and second sets of curvilinear elementsare connected to one another to define a substantially sinusoidalpattern extending circumferentially along the segments, the sinusoidalpattern having an alternating amplitude defined by the first and secondlongitudinal lengths. Alternatively, the substantially “U” shapedelements may have first and second thicknesses or diameters, wherein thefirst thickness is substantially less than the second thickness.

In addition, the connector preferably includes a curve extending atleast partially circumferentially along the circumference defined by theplurality of segments. More preferably, the connector defines asinusoidal shape adapted to extend and compress axially substantiallyevenly when the adjacent segments are subjected to a predeterminedbending force. Although the connector may extend and compress, theconnector preferably does not deform substantially when the stent isexpanded, i.e., the connector remains substantially stationary anddistinct from the adjacent segments and does not become part of thecellular structure itself. Furthermore, the connector preferablyincludes a pair of connectors located opposite one another on thecircumference for facilitating articulation of the adjacent segmentssubstantially transverse about the longitudinal axis.

Thus, an important aspect of the present invention is to provide a stentthat includes a substantially tubular member plastically deformablebetween contracted and enlarged conditions, including a plurality ofcylindrical segments and connectors for facilitating articulation of theadjacent cylindrical segments about the longitudinal axis, for example,when the stent is bent during delivery in a curved body passage and/orthat substantially uniformly scaffolds the wall of the body passage.

In another aspect, the present invention is directed to a device fordelivering an expandable stent, such as that previously described, to asite within a patient's body. The device includes an elongate memberhaving proximal and distal ends, a nose cone on the distal end, and anexpandable member on the elongate member proximate to the nose cone forreceiving an expandable stent thereon. The nose cone has a widenedportion and a tapered distal tip to facilitate insertion along a bodypassage.

The stent delivery device also preferably includes an outer sheathslidable over the elongate member, the outer sheath including a lumenfor receiving the elongate member therethrough. The outer sheathincludes a distal end having a diameter substantially similar to thewidened portion of the nose cone for substantially sealing the lumenwhen the distal end of the outer sheath engages the widened portion ofthe nose cone and/or to provide a substantially smooth transitiontherebetween to facilitate advancement of the stent delivery devicethrough the body passage. In addition, the outer sheath may include oneor more perfusion holes extending between an outer surface of the outersheath and the lumen for allowing continued perfusion of fluid along thebody passage during stent delivery. The nose cone may also includeperfusion holes proximal and distal of the widened portion.

In addition, the stent delivery device also may include a shoulder onthe elongate member proximate the expandable member. The shoulderpreferably has a blunt distal edge for engaging a proximal end of anexpandable stent received on the expandable member to preventsubstantial proximal movement of the expandable stent. The shoulder mayalso include a substantially tapered proximal edge to facilitatewithdrawal of the elongate member from a body passage.

The device may be used in a method for implanting a prosthesis or stentwithin a curved region of a body passage, the stent including aplurality of cylindrical segments and a plurality of connectorsextending between adjacent segments, as previously described. The stentis placed in a contracted condition on a distal end of a stent deliverydevice, the distal end of the stent delivery device is advanced alongthe body passage, and the stent is positioned within the curved region.The stent is then expanded, first to an intermediate enlarged conditionto substantially eliminate localized radial forces, and then further toa final enlarged condition, the circumferential pattern of alternatingcurvilinear elements expanding substantially evenly about acircumference of the stent to scaffold the curved region. The stentdelivery catheter may then be withdrawn from the body passage, leavingthe stent substantially permanently implanted within the curved region.

More preferably, the stent delivery device is used in a method fordelivering an expandable stent to a selected delivery site within apatient's body, for example, within the cardiovascular system. The stentdelivery device includes an elongate member having an expandable memberon its distal end, a tapered nose cone, a proximal shoulder, and anouter sheath for slidably receiving the elongate member therein. Thestent is placed in a contracted condition on the expandable member, andthe elongate member is inserted into the outer sheath to cover thestent. The distal end of the elongate member is advanced along a bodypassage within the patient's body, and the stent is positioned at theselected delivery site. The outer sheath is withdrawn proximally toexpose the stent at the selected delivery site, and the stent isexpanded to an enlarged condition with the expandable member. The methoddescribed may be particularly useful for creating and/or maintaining achannel connecting a vein to an adjacent artery, preferably in thecoronary system.

Other objects and features of the present invention will become apparentfrom consideration of the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view of a preferred embodiment of an unexpanded stentin accordance with the present invention.

FIG. 1B is a side view of the stent of FIG. 1A expanded to a firstenlarged condition.

FIG. 1C is a side view of the stent of FIG. 1A expanded to a secondenlarged condition.

FIG. 2 is a flat view of the unexpanded stent of FIG. 1 unrolled to moreclearly show the configuration of the stent elements.

FIG. 3A is a perspective view of the stent of FIG. 1B, expanded to thefirst enlarged condition.

FIG. 3B is a perspective view of the stent of FIG. 1B, with a proximalportion of the stent further expanded to a second enlarged condition.

FIG. 4A is a cross-sectional side view of two adjacent blood vesselswith a guide wire placed through a channel between the vessels.

FIGS. 4B and 4C show a balloon catheter delivered over the guide wireand positioned between the vessels of FIG. 4A, with the ballooncollapsed for delivery and expanded for dilating the channel,respectively.

FIG. 4D shows a stent delivery device being delivered over the guidewire, after withdrawal of the balloon catheter of FIGS. 4B and 4C.

FIGS. 4E and 4F show a stent being positioned across the channel of FIG.4D with the assistance of markers on the stent delivery device, and anouter sheath being retracted to expose the stent, respectively.

FIGS. 4G and 4H show a balloon on the stent delivery device of FIGS. 4Eand 4F being inflated to expand the stent to its enlarged condition, andbeing deflated to facilitate withdrawal of the stent delivery device,respectively.

FIG. 4I shows the stent delivery device of FIGS. 4G and 4H beingwithdrawn, leaving the stent in place across the channel.

FIG. 5A is a side view of a preferred embodiment of a stent deliverydevice, with a stent placed in a collapsed condition over a balloon onthe stent delivery device.

FIG. 5B is a cross-sectional side view the stent delivery device of FIG.5A.

FIG. 6A is a cross-sectional side view of another preferred embodimentof a stent delivery device with a nose cone, a backstop, and an outersheath.

FIG. 6B is a cross-sectional side view of the distal end of the stentdelivery device of FIG. 6A, with the outer sheath substantially engagingthe nose cone.

FIG. 6C is an alternative embodiment of the stent delivery device ofFIG. 6B, with a tactile indicator protrusion on the outer sheath.

FIG. 6D is another alternative embodiment of the stent delivery deviceof FIG. 6B, with a dilation balloon on the outer sheath.

FIG. 7A is a side view of another preferred embodiment of a stentdelivery device, similar to FIG. 6, with a plurality of perfusion holesthrough the outer sheath and the nose cone.

FIG. 7B is a detail of the distal end of the stent delivery device ofFIG. 7A, showing fluid flow through the perfusion holes.

FIG. 7C is a side view of the stent delivery device of FIG. 7A placedbetween two adjacent blood vessels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, FIGS. 1-3 show a preferred embodiment of animplantable prosthesis or stent 10 in accordance with the presentinvention. Generally, the stent 10 includes a plurality of expandablecylindrical segments or “cells” 12 and a plurality of articulatingconnectors 14 which extend between adjacent cells 12.

Preferably, the stent 10 is an initially solid tubular member, defininga longitudinal axis 16 and a circumference 18, that is preferably formedfrom a substantially plastically deformable material, such as stainlesssteel Type 316L, tantalum, MP35N cobalt alloy, or Nitinol. The walls ofthe tubular member are selectively removed by high precision cutting,e.g. laser cutting, chemical etching, water jet cutting or standard toolmachining, to provide the pattern of cells 12 and connectors 14described in detail below. Alternatively, the stent may be formed from aflat sheet of material that is rolled and axially fused together aftercreating the pattern of cells 12 and connectors 14.

With particular reference to FIG. 2, each cell 12 includes analternating circumferential pattern of curvilinear elements or struts 20which extends about the circumference 18. Preferably, the alternatingpattern of curvilinear elements 20 includes a first set of curvilinearelements 22, having a first resistance to expansion, that alternateswith a second set of curvilinear elements 24, having a second resistanceto expansion that is substantially higher than that of the first set ofcurvilinear elements 22. The first and second resistances to expansioncorrespond to the resistance of the curvilinear elements 22, 24 toplastic deformation, i.e., once first and second plastic yield strengthsof the curvilinear elements 22, 24, respectively, are exceeded.Alternatively, more than two sets of curvilinear elements may beprovided in the circumferential pattern, if the sets are alternated toprovide a cyclical pattern about the circumference 18.

More preferably, the first and second sets of curvilinear elements 22,24 are substantially “U” shaped elements, extending substantiallyparallel to the longitudinal axis 16, connected to one another to form acontinuous alternating amplitude sinusoidal or “zigzag” segment thatextends about the circumference 18 of the cells 12. The first set ofcurvilinear elements 22 has a first longitudinal length or “amplitude”26 that is substantially longer than a second longitudinal length oramplitude 28 of the second set of curvilinear elements 24, therebyproviding a longer relative lever arm that results in the lowerresistance to radial expansion, as will be appreciated by those skilledin the art. In a preferred form, the first longitudinal length is about0.045 inches, and the second longitudinal length is about half the firstlongitudinal length.

In an alternative form, the first and second sets of curvilinearelements 22, 24 may have similar longitudinal lengths, but may havedifferent thicknesses or diameters (not shown). For example, the firstset of curvilinear elements may have a first thickness that issubstantially smaller than a second thickness of the second set ofcurvilinear elements, thereby providing the first and second resistancesto expansion, respectively. Alternatively, a combination of differentshapes, lengths and/or thicknesses may be provided for the first andsecond set of curvilinear elements that result in the first and secondresistances to expansion, as will be appreciated by those skilled in theart.

Due to the differences in resistances to expansion of the first andsecond sets of curvilinear elements 22, 24, the cells 12 may beexpandable between a contracted condition (FIG. 1A), an intermediate orfirst expanded condition (FIG. 1B), and a final or second expandedcondition (FIG. 1C). The first expanded condition is achieved when aradial force at least as great as the first plastic yield strength isapplied to the cells 12, and the second expanded condition is achievedwhen a radial force at least as great as the second plastic yieldstrength is applied to the cells 12, as is described more particularlybelow.

Extending between the cells 12, the connectors 14 generally include acurve that extends at least partially circumferentially along thecircumference 18 of the stent 10, i.e., substantially transverse to thelongitudinal axis 16. In a preferred embodiment, the connectors 14define a sinusoidal shape 30. The sinusoidal shape 30 is adapted toexpand and contract substantially evenly parallel to the longitudinalaxis 16 when the adjacent cells 12 are subjected to bending.

In addition, the sinusoidal shape 30 also maximizes surface engagementof a body passage. The transverse portions 30 a, 30 b extendsubstantially transversely with respect to the longitudinal axis 31,thereby providing additional circumferential scaffolding to minimizegaps circumferentially between the connectors 14 which may otherwiseresult due to the smaller length of the second set of curvilinearelements 24.

Preferably, the connectors 14 are provided in pairs located opposite oneanother about the circumference 18 of the cells 12, and more preferablyfour connectors 14 are provided that are evenly spaced about thecircumference 18 between each pair of adjacent cells 12. When the stent10 is subjected to bending, the pairs of connectors 14 facilitatearticulation of the adjacent cells 12, thereby resulting in asubstantially uniform cross-section interior lumen 32 within the stent10 that substantially scaffolds the vessel wall and minimizes thecreation of gaps between adjacent cells 12.

When the stent 10 is bent substantially transversely with respect to thelongitudinal axis 16, as shown in FIGS. 3A and 3B, it is preferred thatan outer radiused portion 36 of the stent 10 extend longitudinally andan inner radiused portion 34 compress longitudinally to minimize anyoverall change in length of the stent 10. The sinusoidal shape 30 of thepair of connectors 14 facilitates this by providing a similar resistanceto deformation when subjected to either tensile or compressive forces.Thus, a pair of connectors 14 on the outer and inner portions 34, 36 ofa bend may extend and compress longitudinally substantially evenly,thereby facilitating articulation of the stent 10 substantially evenlyabout the longitudinal axis 16 and substantially eliminating thecreation of gaps between the adjacent cells 12.

The substantially “S” shape of the stent 10 shown in FIGS. 3A and 3B maybe a particularly useful configuration for the final enlarged condition.In this configuration, the stent 10 may be used to maintain a channelbetween adjacent body passages, such as adjacent blood vessels (notshown), as described further below. More particularly, as shown in FIG.3B, the stent 10 may be expanded to the first enlarged condition on adistal end 10 a, and to the second enlarged condition on a proximal end10 b to facilitate placement between adjacent blood vessels havingdifferent diameters, e.g. between an artery and a vein, respectively(not shown). Additional information on procedures for creating and/ormaintaining channels between adjacent body passages may be found in U.S.patent application Ser. No. 08/970,694 filed Nov. 14, 1997, thedisclosure of which is expressly incorporated herein by reference.

Returning to the cells 12, the alternating pattern 20 of curvilinearelements described above is an important feature of a stent 10 inaccordance with the present invention, which may be illustrated bygenerally describing the deployment of the stent 10. The stent 10 isdelivered to a selected delivery site within a body passage, such as ablood vessel (not shown), using a stent delivery device, such as thatshown in FIGS. 5A and 5B and designated as 100. The stent deliverydevice 100 includes an elongate catheter body or tubular member 102having a distal end 104 adapted for insertion into a body passage.

A balloon 108 or other expandable member is attached to or otherwiseprovided on the catheter body 102, preferably with a marker 106, such asa radiopaque marker, on the catheter body 102 in a predeterminedrelationship with the balloon 108. The balloon 108 is preferably formedfrom an inelastic material, such as polyethylene, that expands to adiameter preselected to correspond to the diameter of the body passageinto which the stent 10 is to be implanted. Because of its inelasticity,the uninflated balloon 108 is typically wrapped around the elongatemember 102, e.g., by rolling the balloon 108 circumferentially.

The stent 10 is compressed over the balloon 108, and delivered during asurgical procedure, such as the preferred method described below. Oncethe stent 10 is advanced and properly positioned at the delivery site,the balloon 108 is inflated to expand the cells 12 of the stent 10 (notshown in FIGS. 5A and 5B). As the balloon 108 inflates, it may notunwrap substantially uniformly, causing the radial forces applied to thecells 12 to be initially localized, i.e., certain portions of the cells12 may be expanded more than others.

Because the first set of curvilinear elements 22 (not shown in FIGS. 5Aand 5B) of the cells 12 has a lower resistance to expansion than thesecond set of curvilinear elements 24, the first set of curvilinearelements 22 expands more quickly than the second set of curvilinearelements 24, thereby expanding the cells 12 to their intermediateenlarged condition (FIG. 1B). After the balloon 108 is substantiallyunwrapped, it may be inflated further, thereby applying a substantiallyuniform radial force to the cells 12. When this substantially uniformradial force is applied to the alternating resistances to expansion ofthe first and second sets of curvilinear elements 22, 24, the radialforce of the balloon 108 is distributed substantially circumferentiallyevenly about the circumference of the cells 12, thereby expanding thecells 12 to the final enlarged condition (see FIG. 1C) whilesubstantially eliminating localized over-expansion that can create gapswithin the cells 12.

In addition, although the connectors 14 may extend and compress as theadjacent cells 12 are expanded, e.g., within a curved body passage, theconnectors 14 preferably do not deform substantially. Stateddifferently, the connectors 14 preferably remain substantiallystationary and distinct from the adjacent segments 12, i.e., retaining asubstantially sinusoidal shape, and do not become part of the cellularstructure of the stent 10.

Turning to FIGS. 4A-4I and 6A-6D, a system and method for delivering astent 10 in accordance with the present invention is illustrated. In apreferred embodiment, shown particularly in FIG. 6A, a stent deliverydevice 200 for delivering an expandable stent 10 is provided, whichincludes an elongate catheter body 202 with an expandable balloon 208, anose cone 212, a shoulder 216 thereon, and an outer sheath 220. Thecatheter body 202 has a proximal end 203, a distal end 204, and a lumen210 extending therebetween for directing the catheter body 202 over aguide wire 110 (FIGS. 4A-4I). The materials and dimensions of thecatheter body 202 are otherwise similar to conventional catheterdevices, as will be appreciated by those skilled in the art.

The nose cone or dilator 212 is attached to the distal end 204 of thecatheter body 202, and has a tapered distal tip 216 to facilitateadvancement along a body passage and/or to dilate partially occludedregions of the body passage. The nose cone 212 may be provided fromsubstantially flexible and or resilient material, such as Pebax®,polyurethane, polyethylene, or nylon, adapted to minimize damage totissue during advancement of the stent delivery device 200 within thebody passage. The nose cone 212 has a widened portion 214, preferablywith a diameter of not more than about 6 French, thereby allowingpercutaneous insertion into a blood vessel, such as into a patient'svasculature. The nose cone 212 may have a tapered proximal end 218, oralternatively a substantially blunt proximal end (not shown) forengaging the distal edge 36 of the stent 10 to prevent substantialdistal movement of the stent 10 with respect to the catheter body 202.

The balloon 208 is attached to the catheter body 202 proximate to thenose cone 212. The balloon 208 preferably has an annular shape that isformed from a substantially inelastic material, such as polyethylene ornylon, and preferably has a predetermined inflated diameter selected tocorrespond to the size of the stent 10 in its enlarged condition and/orto the body passage into which the stent 10 is to be implanted, andlength selected to correspond to the length of the stent 10, as will beappreciated by those skilled in the art. The interior of the balloon 208communicates with an inflation lumen (not shown) which extendsproximally from the distal end 204 of the catheter body 202 to a sourceof inflation media, such as saline (not shown). Alternatively, otherinflatable or mechanically expandable members may be provided instead ofthe balloon 208.

The shoulder or backstop 213 is provided on the catheter body proximatethe balloon 208. The shoulder 213 has a substantially blunt distal edge214 for engaging a proximal end 36 of the stent 10 received on theballoon 208 to prevent substantial proximal movement of the stent 10.The shoulder 213 also preferably has a tapered proximal edge 216 tofacilitate withdrawal of the catheter body 202 from within a bodypassage. The shoulder 213 may be integrally formed as part of thecatheter body 202 or it may be a separate attached member.

The catheter body 202 may also include one or more markers, such as theradiopaque marker 206, thereon. The marker 206 preferably has apredetermined relationship with the balloon 208, and consequently to thestent 10 placed thereon, to facilitate positioning of the stent 10 atthe delivery site. For example, the marker 206 may be placed at amidpoint of the balloon 208 as shown, thereby allowing the stent 10 tobe centered across a body passage. Alternatively, a marker may beprovided adjacent to either end of the balloon 208, i.e. adjacent theproximal end 34 and/or the distal end 36 of the stent. In a furtheralternative, the nose cone 212 and/or the shoulder 213 may be providedfrom a radiopaque material or may be marked at a predetermined locationthereon.

The outer sheath 220 is an elongate member having a proximal end 222, adistal end 224, and a lumen 226 therein, that is slidable over thecatheter body 202, i.e., the catheter body 202 may be slidably receivedwithin the lumen 226 in the outer sheath 220. Preferably, the distal end224 of the outer sheath 220 is tapered to facilitate advancement along abody passage, and more preferably, the distal end 224 has an innerdiameter similar to the widened portion 214 of the nose cone 212. Thus,when the catheter body 202 is received within the outer sheath 220, thedistal end 224 may engage the widened portion 214 to provide asubstantially smooth surface which may facilitate advancement of thestent delivery device 200 through a body passage. In particular, theresulting smooth surface may facilitate advancement of the nose cone 212and outer sheath 220 through a channel created between two adjacentblood vessels, with minimized risk of snagging or getting caught onloose tissue in the channel. In addition, the outer sheath 220 mayengage the nose cone 212 to substantially seal the lumen 224 and therebyprevent fluid contact with the stent 10 until exposed at the deliverysite.

The stent delivery device 200 may also include a handle or controlmechanism 230 on the proximal end 203 of the catheter body 202. Thehandle 230 may include an outer housing 232 to which the proximal end203 of the catheter body 202 is fixed, and a slider 234 slidable withrespect to the housing 232, i.e., within a cavity 236 therein. Theproximal end 222 of the outer sheath 220 may be attached to the slider234, such that when a thumb grip 238 or other slider control is engagedand drawn proximally, the outer sheath 220 may be withdrawn proximally,for example, to expose the balloon 208 when a stent 10 is initiallyplaced thereon or to expose the stent 10 at the delivery site.

With particular reference to FIGS. 4A-4I and 6A, the stent deliverydevice 200 may be used in a method for creating and/or maintaining achannel between adjacent body passages, such as a channel 262 between acoronary vein 252 and a coronary artery 254. A guide wire 110 ispercutaneously introduced into a passage in a patient's body, such as afemoral vein, advanced into the coronary vein 252, and placed throughthe intervening tissue 260 into the adjacent coronary artery 254 toprovide a channel 262 (FIG. 4A).

A balloon catheter 280 is advanced over the guide wire 110 until amarker 284 on the balloon catheter 280 is positioned in a predeterminedrelationship with the channel 262, e.g., the marker 284 may be centeredunder a balloon 282 on the balloon catheter 280 (FIG. 4B). The balloon282 is then inflated to dilate the channel 262, i.e., to push thesurrounding tissue 260 adjacent the channel 262 away and provide across-section sufficiently large to allow substantially unimpaired bloodflow between the artery 254 and the vein 252 (FIG. 4C). The balloon 280may then be deflated, and the balloon catheter 280 withdrawn over theguide wire 110 and out of the body.

Alternatively, other methods may be used to enlarge the channel 262instead of using the balloon catheter 280. For example, the channel 262may be debulked by removing intervening tissue 260 using energy, such aslaser or radio frequency (RF) energy, or by cutting or slicing throughthe intervening tissue 260, with over-the-guide wire instruments, untila desired size channel 262 is produced. In further alternatives, otherdilation devices may be used, such as mechanically expandable members,or the nose cone 212 of the stent delivery catheter 200, as describedbelow.

A stent 10 having a predetermined length and enlarged conditiondiameters is selected to correspond with the configuration of thechannel 262, the artery 254 and/or the vein 252. The stent 10 may bepreselected if the delivery site is known prior to the commencement ofthe procedure, or the stent 10 may be selected once the site for thechannel 262 is selected during the course of the procedure. The stent 10is then placed on a stent delivery device 200, as shown in FIG. 6A.Generally, the stent delivery device 200 is selected to correspond tothe selected stent 10 and delivery site, i.e., based on the diameter ofthe catheter body 202, the inflated balloon 208 and/or the outer sheath220.

The balloon 208 may be rolled or otherwise wrapped around the catheterbody 202, and the stent, in its contracted condition, is placed over theballoon 208, for example, by manually compressing the stent 10 onto theballoon 208. The outer sheath 220 may then be advanced over the catheterbody 202 until its distal end 224 substantially engages the nose cone212, thereby substantially sealing the stent 10 within the lumen 226 inthe outer sheath 220. Alternatively, the stent 10 may be sufficientlysecured to the catheter body 202 such that the stent 10 may be deliveredwithout the outer sheath 220, as shown, for example, in FIGS. 5A and 5B,as will be appreciated by those skilled in the art.

The stent delivery device 200 is then advanced over the guide wire 110until the nose cone 212 passes through the channel 262 (FIG. 4D). Thetapered distal tip 216 of the nose cone 212 facilitates the advancementof the stent delivery catheter 200 through the channel 262. The widenedportion 214 of the nose cone 212 may have a size larger than the channel262 to further dilate the channel 262 as the nose cone 212 is advancedtherethrough. Alternatively, the nose cone 212 may be used to dilate thechannel 262 in place of the balloon catheter 280. For example, as thenose cone 212 is advanced through the channel 262, the interveningtissue 260 may be pushed substantially away to dilate the channel 262,although it may be necessary to withdraw and advance the nose cone 212multiple times to effectively dilate the channel 262.

In a further alternative, shown in FIG. 6D, the outer sheath 220 mayinclude a dilation balloon 228 proximate its distal end 224. Thedilation balloon 228 may be similar to the dilation balloon 280described previously, but attached around the outer sheath 220,preferably such that the outer sheath 220 and unexpanded balloon 228have a diameter of about twelve French or less. When the outer sheath220 and the nose cone 212 are advanced and contact the undilated channel262, or other partial obstruction, the balloon 228 may be inflated toopen the body passage, and then deflated to allow further advancement orwithdrawal.

The substantially smooth transition between the outer sheath 220 and thenose cone 212 is an important feature, which may minimize snagging orotherwise damaging the surrounding tissue 260 with the distal end 224 ofthe outer sheath 220. The smooth transition may also minimize catchingthe distal end 224 of the sheath 220 on loose tissue, a lesion or otherconstrictions in the body passage which may prevent further advancementof the stent catheter device 200.

In addition, because the outer sheath 220 substantially contains thestent 10 therein, the outer sheath 220 may also substantially minimizepotential damage to vessel walls and the tissue 260 surrounding thechannel 262, which may otherwise occur if an exposed stent 10 isadvanced therethrough. The outer sheath 220 may also substantiallyprotect the stent 10 itself during advancement over the guide wire 10.For example, the outer sheath 220 may protect the stent 10 from beingdislodged from the stent delivery device 200 prematurely, i.e., at alocation other than the intended delivery site. Thus, the outer sheath220 may substantially eliminate the risk of emergency surgicalprocedures to recover loose stents 10. Alternatively, if the outersheath 220 is eliminated, the blunt edge 214 of the shoulder 213 and/orof the nose cone 212 may sufficiently protect the stent 10, and preventsubstantial axial movement of the stent 10 as it is being advancedthrough the body passage.

The stent 10 may be positioned across the channel 262 with the aid ofmarkers 206 a, 206 b. Preferably, the markers 206 a, 206 b areradiopaque, such that they may be viewed using fluoroscopy, or otherexternal imaging methods. The markers 206 a, 206 b, shown in FIGS. 4Eand 4F, for example, are provided on the nose cone 212 and the shoulder213 to approximate the location of the proximal and distal edges 34, 36,respectively, of the stent 10.

Alternatively, as shown in FIG. 6B, the outer sheath 220 may include oneor more protrusions 227 for assisting in positioning the stent 10 acrossthe channel 262 (not shown in FIG. 6B). For example, the protrusion 227may be a substantially rounded annulus molded directly onto the outersheath 220 at a predetermined location with respect to the stent 10,e.g., at a midpoint thereof. The protrusion 227 may allow a user todetect when the outer sheath 220, and consequently the stent 10, areproperly positioned across the channel 262, for example, based upon theresistance of the protrusion 227 to advancement beyond the channel 262,which may substantially reduce the risk of over-advancing the stent 10beyond the channel 262.

Once the stent 10 is properly positioned, the outer sheath 220 iswithdrawn proximally to expose the stent 10 across the channel 262 (FIG.4F). The balloon 208 may then be inflated, thereby expanding the stent10 to its enlarged condition (FIG. 4G). The inflation of the balloon 208may be performed in two steps, first by inflating the balloon 208 to afirst pressure, thereby expanding the stent 10 to an intermediateenlarged condition and unwrapping the balloon 208 substantially from thecatheter body 202 (not shown), and then by inflating the balloon 208 toa second higher pressure to fully expand the stent 10 to its finalenlarged condition (FIG. 4G).

The balloon 208 may then be deflated (FIG. 4H), and then the stentdelivery device 200 may be withdrawn over the guide wire 110 (FIG. 4I),leaving the stent 10 substantially permanently implanted across thechannel 262. Preferably, the stent 10 substantially engages the lumens256, 258 of the vein 252 and artery 254, respectively, as well as thetissue 260 surrounding the channel 262 to provide a substantiallyunimpaired passage for blood flow between the artery 254 and the vein252.

In one form, the space between the cells 12 and/or between thecurvilinear elements 22, 24 remains substantially open, therebypermitting fluid to pass through the circumference 18 of the stent 10and to continue flowing along the vessel and not cross through thechannel 262 into the other vessel. For example, when a coronary vein isused to bypass an adjacent occluded coronary artery, it may be desirableto continue to allow some blood flow along the coronary artery toperfuse the occluded region. Alternatively, a nonporous membrane (notshown) may be attached about the circumference 18 of the stent 10 todirect all fluid from the source vessel through the channel into theother vessel.

In an alternative method, because of differences in the diameters of thevein 252 and the artery 254, it may desirable to have the final diameterof the enlarged stent 10 vary along its length, as shown in FIGS. 3B and4H. For example, the stent 10 may be selected such that the first orintermediate enlarged condition corresponds to the diameter of theartery 254 and the second enlarged condition corresponds to the diameterof the vein 252. The balloon 208 may have a diameter that varies alongits length, e.g., the diameter may be larger on a proximal portion ofthe balloon 208 (not shown), to facilitate proper expansion of the stent10. Alternatively, the balloon 208 may be used to expand the stent 10 tothe first enlarged condition, using the method previously described, andthen a second balloon may be advanced over the guide wire 110 to expandspecific cells 12 or portions of the stent 10 to the second enlargedcondition, as will be appreciated by those skilled in the art.

In another alternative, a portion of the stent 10 may be provided from aself-expanding material, e.g., heat treated Nitinol, and another portionmay be provided from a malleable as previously described. For example,it may be desirable to have the proximal end 10 b automatically expandwhen deployed to engage one vessel, while the distal end 10 a may beselectively deformed to engage an adjacent vessel. Preferably, where thestent 10 is used to maintain a channel between a vein and an adjacentartery, the proximal end 10 b may be self-expanding, thereby allowingthe stent 10 to automatically expand to engage the wall of the vein. Theproximal end 10 b of the stent 10 may automatically enlarge tocontinuously engage the wall of the vein, thereby accommodatingsubsequent venous expansion which may occur over time as the vein issubjected to arterial pressure. The distal end 10 a may be plasticallydeformed, for example, using a balloon catheter, to a desired enlargedcondition, as described previously.

In another embodiment, particularly with regard to using the prosthesis10 between two vessels to form an anastomosis therebetween, it may bedesirable to form the prosthesis 10 and the resulting connection in moreovular shape than is desired during simple intraluminal placement wherethe prosthesis 10 may be generally circular. Elliptical connections inthis particular application may promote a better physiologic response tothe implant, by lessening turbulence in the blood flow and imitating amore natural vessel condition.

Turning to FIGS. 7A-7C, an alternative embodiment of a stent deliverydevice 300 is shown that provides continued blood perfusion during stentdelivery in accordance with another aspect of the present invention.Most of the elements of this device are similar to the embodiment shownin FIG. 6A, with like elements having reference numbers increased by100.

In particular, the stent delivery device 300 includes a catheter body302, a nose cone 312, and an outer sheath 320. The outer sheath 320includes one or more perfusion holes 350 that extend from its outer wallto a lumen 326 for receiving the catheter body 302 therethrough, or to aseparate lumen (not shown). The nose cone 312 also includes one or moreperfusion holes 352, 354 proximal and distal to the widened portion 314,with a perfusion lumen 356 (shown in phantom in FIG. 7B) extendingbetween them.

For example, as shown in FIG. 7C, the stent delivery device 300 may bepositioned across a channel 262 between a vein 252 and an artery 254,for example during the stent delivery method described above. The outersheath 320 may substantially occlude the artery 254, such that withoutthe perfusion holes 350, blood flow along the artery 254 would besubstantially impaired. Because of the perfusion holes 350, 352, 354,however, blood may continue to travel along the artery 254, for example,first by entering the lumen 326 of the outer sheath 320 through theperfusion holes 350. The blood may then enter the proximal or inletperfusion holes 352 in the nose cone 312, pass through the perfusionlumens 356, and then reenter the artery 254 through the distal or outletperfusion holes 354 to continue downstream.

While the invention is susceptible to various modifications, andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formsor methods disclosed, but to the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the appended claims.

What is claimed is:
 1. A method of delivering an expandable stent acrossa channel connecting a vein to an adjacent artery, the method comprisingthe steps of: providing a stent delivery device including an elongatemember comprising a distal end, the elongate member comprising anexpandable member and a nose cone on the distal end, and a stent in acontracted condition on the expandable member; inserting the elongatemember into an outer sheath to cover the stent, the outer sheathengaging the nose cone to provide a substantially smooth transitiontherebetween; advancing the distal end of the elongate member along thevein until the nose cone is advanced into the channel; positioning thestent across the channel; withdrawing the outer sheath proximally toexpose the stent within the channel; expanding the stent to an enlargedcondition within the channel with the expandable member; and withdrawingthe elongate member from the patient's body.
 2. The method of claim 1,wherein the elongate member includes a shoulder proximate the expandablemember for preventing substantial proximal movement of the stentreceived thereon.
 3. The method of claim 1, wherein the nose cone atleast partially dilates the channel when the distal end of the catheterbody is advanced therethrough.
 4. The method of claim 1, wherein theouter sheath includes perfusion holes therethrough to allow continuedflow of blood along the artery when the stent is positioned across thechannel.
 5. The method of claim 1, wherein the nose cone includesperfusion holes therethrough to allow continued flow of blood along theartery when the stent is positioned across the channel.
 6. The method ofclaim 1, wherein the stent delivery device includes an externallyobservable marker, and wherein the marker is observed when the stent ispositioned across the channel.
 7. The method of claim 1, furthercomprising the step of dilating the channel with an expandable member onthe outer sheath.
 8. The method of claim 1, wherein the outer sheathincludes an outer protrusion, and wherein the protrusion produces atactile indication when the stent is positioned across the channel.
 9. Amethod for delivering a stent across a channel between two adjacentblood vessels, the method comprising: providing a delivery devicecomprising an elongate member including a nose cone on a distal end ofthe elongate member, a stent in a contracted condition on the distal endadjacent the nose cone, and a sheath covering the stent, the sheathengaging the nose cone to provide a substantially smooth transitiontherebetween; advancing the distal end of the elongate member along thefirst blood vessel until the nose cone is advanced into the channel;positioning the stent across the channel; withdrawing the sheath toexpand the stent to an enlarged condition to engage tissue surroundingthe channel; and withdrawing the elongate member from the patient'sbody.
 10. The method of claim 9, wherein the nose cone at leastpartially dilates the channel when the nose cone is advanced through thechannel.
 11. The method of claim 10, further comprising withdrawing andadvancing the nose into the channel multiple times to dilate thechannel.
 12. The method of claim 9, wherein the elongate membercomprises an expandable member on the distal end, the stent beingprovided on the expandable member, and wherein the step of withdrawingthe sheath to expand the stent comprises: withdrawing the sheath toexpose the stent within the channel; and expanding the expandable memberto forcibly expand the stent to the enlarged condition to substantiallyengage tissue surrounding the channel.
 13. The method of claim 9,wherein the stent is at least partially self-expanding, and wherein thestep of withdrawing the sheath to expand the stent comprises withdrawingthe sheath to expose the stent, whereupon at least a portion of thestent expands automatically to the enlarged condition.
 14. The method ofclaim 9, further comprising creating the channel between the first andsecond blood vessels.
 15. The method of claim 14, wherein the step ofcreating the channel comprises advancing a guidewire through the tissuebetween the first and second blood vessels.
 16. The method of claim 15,wherein the step of advancing the elongate member comprises advancingthe elongate member over the guidewire, thereby advancing the nose coneover the guidewire into the channel.
 17. The method of claim 9, whereinthe step of advancing the distal end of the elongate member comprisesadvancing the nose cone through the channel into the second bloodvessel, and wherein at least one of the nose cone and the sheathincludes perfusion holes therethrough to allow continued flow of bloodalong the second blood vessel.
 18. The method of claim 9, wherein thedelivery device includes an externally observable marker, and whereinthe marker is observed when the stent is positioned across the channel.19. The method of claim 9, further comprising the step of dilating thechannel with an expandable member on the sheath.
 20. The method of claim9, wherein the sheath includes an outer protrusion, and wherein theprotrusion produces a tactile indication when the stent is positionedacross the channel.
 21. The method of claim 9, wherein the advancingstep comprises advancing the distal end of the elongate memberpercutaneously into a patient's vasculature until the distal end isdisposed within the first blood vessel.
 22. A method for delivering astent across a channel between two adjacent blood vessels of a patient,the method comprising: providing a delivery device comprising anelongate member including a nose cone and an expandable member on adistal end of the elongate member, a stent in a contracted condition onthe expandable member on the distal end adjacent the nose cone, and asheath covering the stent, the sheath engaging the nose cone to providea substantially smooth transition therebetween; creating a channelthrough tissue between first and second adjacent blood vessels;advancing the distal end of the elongate member from a percutaneousentry site into the patient's vasculature and through the first bloodvessel until the nose cone is advanced into the channel; positioning thestent across the channel such that the stent extends into at least oneof the first and second blood vessels; withdrawing the sheath to exposethe stent within the channel; expanding the expandable member to expandthe stent to an enlarged condition to engage tissue surrounding thechannel; and withdrawing the elongate member from the patient's body.23. The method of claim 1, wherein the stent extends into at least oneof the vein and the artery when the stent is expanded within thechannel.